The present invention relates to an automatic piano for performing music through automatic driving of a keyboard and a method and program for automatically operating a key on a keyboard. More particularly, the present invention relates to a technique for improving the reproducibility of a music performance executed by successive key depression operation.
Generally, automatic pianos execute an automatic performance by selectively exciting solenoids, provided in corresponding relation to keys of an acoustic piano, on the basis of performance information, to thereby drive the corresponding keys so that hammers corresponding to the driven keys strike corresponding strings; in this way, an automatic performance of the automatic piano is executed. String striking intensity of the hammer corresponds to a driven velocity of the key that in turn corresponds to a level of a current supplied to the solenoid. In order to reproduce a performance executed through key depression operation by a human player on such an automatic piano, it is desirable to accurately reproduce trajectories of individual keys during the performance so as to expressively describe delicate nuances of the music piece and expression of tones. In this regard, some of the conventionally-known automatic piano are constructed to, on the basis of performance data to be reproduced, determine velocity information (i.e., reference velocities) at predetermined points (i.e., reference points) along a movement trajectory of each of the keys, generate trajectory data of the key corresponding to a desired trajectory type (linear, parabolic or the like), and then drive the corresponding solenoid in accordance with the trajectory data (for example, Japanese Patent Application Laid-open Publication No. HEI-7-175472). Further, among the conventionally-known automatic pianos of the above-mentioned type are one which is constructed to reproduce a so-called half-stroke performance where release operation of a key is started before the key is completely depressed to its lower end position or where depression operation of a next key is started during depression operation of a key. More specifically, this conventional automatic pianos calculates, along with trajectory data of linear trajectories (constant velocity trajectory) during depression and release operation of a key, a “shortcut (or shortened) trajectory” corresponding to a second-order curve representative of velocity variation of the key and drives the key, in accordance with the calculated shortcut trajectory, during a transition from the depression phase to the release phase of the key, so as to continuously vary the velocity of the key (for example, Japanese Patent Application Laid-open Publication No. HEI-9-81125).
However, in performance reproduction by the conventional automatic pianos, where an operating velocity of a key is to be varied rapidly, particularly where a key is to be depressed in rapid succession, to reproduce, for example, a half-stroke performance, the key tends to get out of control easily, and various inconveniences, such as an excessive increase in the string striking intensity of the hammer, would result. The No. HEI-9-81125 publication proposes avoiding these inconveniences by controlling a key, for example in a half-stroke performance, to move along the shortcut trajectory before the stroke position of the key reaches an intersection between the depressing trajectory and the releasing trajectory. However, if the key is driven in accordance with the shortcut trajectory as disclosed in the publication, the key stroke amplitude unavoidably decreases, which undesirably tends to key depression errors and insufficient successive-key-depression capability.